1996 Chevy Corvette C4 Project Car - Differential Equation

Part 2: Installing Zip Products' HD Dana 36 Rear

In last month's issue, we followed Zip Products technician Keith Wilhelm as he assembled one of the company's heavy-duty Dana 36 differentials. This time around, we'll detail the process of installing the diff and matching cover in our '96 C4 project car. Although most elements of the job should fall well within the comfort zone of a competent mechanic, access to both a lift and a task-specific spring-compression tool is strongly recommended. Lacking all of the foregoing (especially the competence part), we outsourced the project to our Vette-savvy friends at AntiVenom in Seffner, Florida. Follow along now as we cover the highlights of the installation.

Break-inNow that you've spent a few hours swapping in your new heavy-duty differential, you'll want to make sure you break it in properly. Failure to do so can leave you with a diff that whines, chatters, and otherwise impersonates your mother-in-law. Fortunately, Zip includes detailed break-in instructions with every unit it ships, so doing the job right is simply a matter of reading them and doing as you're told.

After filling the diff with fluid and traction additive (remember: no synthetics), take the car out on the road and check for noise. If none is present, continue to drive at a steady 45 to 65 mph for 30 miles, avoiding heavy acceleration and, if at all possible, stopping. Let the rear cool completely, then repeat the process. After three of these 30-mile driving cycles, the rear should be fully broken in. Have your rear alignment specs checked by a qualified tech (preferably one who's worked on Corvettes before), and you're ready to enjoy your new heavy-duty differential. As for us, we'll have driving impressions and drag-strip numbers for you in an upcoming issue.

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1996 Chevy Corvette C4 Project Car - Differential Equation

After raising the car on the lift, AntiVenom tech Casey Willard begins the job by removing the rear wheels.

Next to go is the spare-tire carrier. We decided to leave ours off for good, since the spare itself had long since gone missing. Jettisoning the carrier not only saves weight, it also cleans up the appearance of the car's rear-underbody area. Just be sure to have your AAA card handy in the event of a flat.

Willard then removes the exhaust system and hangers aft of the differential. This provides unfettered access to the car's rear suspension components.

The next step involves decompressing the rear monoleaf. Ideally, you'd use a purpose-built tool for this job, but since AV didn't have one (they're pricey, after all, and C4 suspension work isn't something the shop does every day), Willard was forced to improvise. Although this cobbled tie-down-strap arrangement worked fine in our case, it's not something you should attempt to duplicate at home. Translation: Use the right tool, or have a pro do it for you.

With the spring compressed by the tie-down strap, Willard loosens the castellated nut and bolt that hold it in place. This allows the spring to decompress, as shown here.

With that done, the bolts holding the spring in place can be removed, followed by the spring assembly itself. (In case you're wondering, the control arms were yanked just prior to this step. Your author was coping with a camera-battery failure at the time and didn't manage to snap a photo.)

Willard then disconnects the U-joints from both the driveshaft and the halfshafts.

The tie-rod bolts are removed next, followed by the tie-rod assembly itself.

The last piece holding the differential in place is the torque arm. With it out of the way, the diff cover can be unbolted and the assembly removed from the car as a single unit.

Willard places the diff assembly on jackstands and removes the cover bolts. Sealant around the circumference of the cover should keep it attached to the housing.

To break the seal, Willard gently pries open the housing with a flathead screwdriver. This allows the old fluid to drain out into the pan below.

Here's a close-up shot of the stock Dana 36 cover. Note that it lacks the Dana 44-style bearing-support blocks incorporated into the Zip Products HD cover.

Willard prepares the new differential by applying high-temp silicone sealant along the mating surface of the housing.

With that done, the cover is attached to the housing, and the entire unit is lifted into place with a transmission jack.

These small rectangular blocks-"harmonic dampeners" in engineering parlance-were installed at the factory to help quell driveline noise. You'll need to remove them from your stock differential and reinstall them on the new Zip unit as shown.

We loaded our differential with two quarts of high-quality mineral-based gear lube and one pint of limited-slip additive. These fluids should meet or exceed API GL-5 and GM 1052358 requirements, respectively. Note that Zip advises against using synthetic lubricants during the initial break-in process.

With the differential fully loaded with fluid, the diff and suspension components can be reinstalled in the reverse order of disassembly. Here's a look at our car with everything reattached but the exhaust pipes.

Align the exhaust tips, torque the wheel lugs to 90 ft-lb, and the car is ready to be lowered.

Don't be too concerned if your car looks like this when you're done. This off-road-ready stance is a natural consequence of having unloaded the rear suspension, and it should disappear after a few miles of street driving. You will, however, need to have your rear alignment checked, since it's unlikely that all of the suspension components ended up in exactly the same position as when you started.

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